Abstract

Background

The curveback lineage of guppy is characterized by heritable idiopathic-type spinal curvature that
develops during growth. Prior work has revealed several important developmental similarities
to the human idiopathic scoliosis (IS) syndrome. In this study we investigate structural
and histological aspects of the vertebrae that are associated with spinal curvature
in the curveback guppy and test for sexual dimorphism that might explain a female bias for severe curve
magnitudes in the population.

Methods

Vertebrae were studied from whole-mount skeletal specimens of curved and non-curved
adult males and females. A series of ratios were used to characterize structural aspects
of each vertebra. A three-way analysis of variance tested for effects of sex, curvature,
vertebral position along the spine, and all 2-way interactions (i.e., sex and curvature, sex and vertebra position, and vertebra position and curvature).
Histological analyses were used to characterize micro-architectural changes in affected
vertebrae and the intervertebral region.

Results

In curveback, vertebrae that are associated with curvature demonstrate asymmetric shape distortion,
migration of the intervertebral ligament, and vertebral thickening on the concave
side of curvature. There is sexual dimorphism among curved individuals such that for
several vertebrae, females have more slender vertebrae than do males. Also, in the
region of the spine where lordosis typically occurs, curved and non-curved females
have a reduced width at the middle of their vertebrae, relative to males.

Conclusions

Based on similarities to human spinal curvatures and to animals with induced curves,
the concave-convex biases described in the guppy suggest that there is a mechanical
component to curve pathogenesis in curveback. Because idiopathic-type curvature in curveback is primarily a sagittal deformity, it is structurally more similar to Scheuermann
kyphosis than IS. Anatomical differences between teleosts and humans make direct biomechanical
comparisons difficult. However, study of basic biological systems involved in idiopathic-type
spinal curvature in curveback may provide insight into the relationship between a predisposing aetiology, growth,
and biomechanics. Further work is needed to clarify whether observed sex differences
in vertebral characteristics are related to the female bias for severe curves that
is observed in the population.